The invention relates to a system and method for controlling a vehicle speed transmission, and in particular, for controlling a continuously variable automatic motor vehicle speed transmission.
Conventional control systems for infinitely variable motor vehicle speed transmissions, referred to as CVT control systems, set the setpoint operating point of the speed transmission, which corresponds to a setpoint engine speed, as a function of the accelerator pedal value or of the resulting setpoint engine torque. The control system contains at least two adjustment characteristic curves: one which is configured for an economical, i.e. fuel-saving-operating mode and another which is configured for a driving performance-oriented, sporty operating mode of the motor vehicle. The latter brings about relatively high engine speedsxe2x80x94corresponding to a relatively small transmission ratioxe2x80x94with the same accelerator pedal position, with the result that the driver is provided with a larger margin in terms of the engine torque or accelerator pedal. In such a case, given the same engine output the driver does not need to deflect the accelerator pedal to the same extent as a control operating using the adjustment characteristic curve for the economical operating mode.
In a known method for operating a vehicle with CVT (DE 43 30 391 A1), the transmission ratio of the speed transmission is continuously adjusted using a manually operated activation device, the adjustment of the transmission ratio taking place within the limits of a maximum transmission ratio and a minimum transmission ratio until the manual activation takes place (Tip operating mode).
CVTs which are controlled in this way are technically very flexible but assume that there is a readiness to shift the gears on the part of the driver. Continuous adjustment of the speed transmission ratio contributes, on the one hand, to keeping the engine in the operating range which is the most favorable for consumption, but on the other hand the driver is totally unaccustomed to keeping the engine speed constant, a characteristic which is also known as the xe2x80x9cscooter effectxe2x80x9d. Many drivers prefer the accustomed acoustic characteristics of a motor vehicle with a multi-step reduction gear, especially the association between the engine speed and the travel speed which is perceptible with a multi-step reduction gear. This applies in particular to drivers who prefer a xe2x80x9csportyxe2x80x9d driving style.
In a method of the generic type for controlling an infinitely variable automatic motor vehicle speed transmission, the transmission ratio can be varied as required by means of a manual intervention by the driver (EP 0 848 191 A1). In manual mode, the transmission ratio is controlled here along predefined setpoint trajectories in order to avoid relatively large engine speed jumps.
In one embodiment of the invention, there is a method for controlling an infinitely variable automatic motor vehicle speed transmission. The method includes, for example, automatically setting the transmission ratio of the speed transmission using stored adjustment characteristic curves as a function of a variable which characterizes the engine output, and a variable which characterizes the vehicle speed, and varying the transmission ratio by manual intervention by the driver. The transmission ratio of the speed transmission is set as a stepped deviation from a setpoint engine speed.
In one aspect of the invention, the deviation is subtracted in the case of a positive acceleration as a term from a setpoint engine speed at the static operating point, and a lower engine speed is obtained in the process.
In another aspect of the invention, during a subsequent acceleration procedure, the motor vehicle is accelerated with a fixed transmission ratio i until an upper setpoint engine speed is reached which lies above the setpoint engine speed at the static operating point by an amount equal to the deviation.
In still another aspect of the invention, the deviation is a function of the vehicle speed.
In yet another aspect of the invention, the deviation is a function of a driver evaluation generated by a fuzzy system.
In another aspect of the invention, the deviation is a function of a load evaluation of the vehicle generated by a fuzzy system.
In yet another aspect of the invention, the deviation rises from a minimum value to a maximum value.
In still another aspect of the invention, the deviation is used as a transmission jump in a manual mode of the speed transmission control system.
In one aspect of the invention, given positive acceleration of the motor vehicle, the change in the engine speed is adapted to the acceleration of the motor vehicle.
In another aspect of the invention, a control system for an infinitely variable automatic motor vehicle speed transmission, a circuit to generate adjustment characteristic curves, by which the transmission ratio of the speed transmission is set automatically as a function of the accelerator pedal position and of the vehicle speed, a control device with which the transmission ratio of the speed transmission is varied as required by manual intervention, and a circuit block by which the transmission ratio of the speed transmission is set as a stepped deviation from a setpoint engine speed.